NBSIR 73-1480

Evaluation of Methodology for

Analysis of Halocarbons in the

Upper Atmosphere: Phase I

Ernest E. Hughes, William D. Dorko, and John K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D C. 20234

March 1978

Final Report: Phase I Issued June 1978

Prepared for National Aeronautics and Space Administration

Washington, D.C. 20546

NBSIR 78-1480

EVALUATION OF METHODOLOGY FOR

ANALYSIS OF HALOCARBONS IN THE

UPPER ATMOSPHERE: PHASE I

Ernest E. Hughes, William D. Dorko, and John K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D.C. 20234

March 1978

Final Report: Phase I Issued June 1 978

Prepared for National Aeronautics and Space Administration

Washington, D.C. 20546

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps. Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

CONTENTS

Page

1. INTRODUCTION 1

2. PREPARATION OF SAMPLES 3

3. CYLINDERS AND CYLINDER PREPARATION 4

4. FILLING THE CYLINDER 5

5. HOMOGENEITY VERIFICATION

5.1 Measurement Method and Standards

5.2 Homogeneity Data

6. STABILITY OF SAMPLES 14

7. PARTICIPATION 17

8. RESULTS OF COLLABORATIVE TEST 18

9. CONCLUSION 25

10. ACKNOWLEDGEMENT 26

11. REFERENCES 27

12. APPENDIX 28

l

to
TABLES

Page

1. Analysis of Halocarbon in Each Sample, , , , . . 10

Concentration in Parts per Trillion by Mole

2. Replicate Analyses of Several Samples in ... . 12

Both A and B Series

Concentration in Parts per Trillion by Mole

3. Analysis of Nitrons Oxide in Several Samples,. . 13

Concentration in Parts per Billion by Mole

4. Analysis of Halocarbons in Samples after .... 15

Return, Concentration in Parts per Trillion by

Mole

5. Analysis of Samples for Nitrous Oxide After. . . 17

Return. Concentration in Parts per Billion by

Mole

6 . Analytical Results for N ? 0 Nitrous Oxide .... 19

7. Analytical Results for Fll 20

8 . Analytical Results for F12 21

9. Youden Plot Data 24

FIGURES

1. Schematic Diagram of System for Filling Sample . 30

Cyl inders

2. Youden Plot of Data for Nitrous Oxide 31

3. Youden Plot of Data for Tr ichlorof luoromethane . 32

(F- 1 1

)

4. Youden Plot of Data for Dif luorodichloromethane . 33

(F-12)

ii
EVALUATION OF METHODOLOGY FOR ANALYSIS OF HALOCARBONS

IN THE UPPER ATMOSPHERE: PHASE I

Final Report, March 1978

ABSTRACT

This report describes the results of a collaborative test to evaluate the state-of-the-art

of measurement of the concentrations of halocarbons

and nitrous oxide in the upper atmosphere. The

collaborative test was the first phase of a program

intended to improve the reliability of measurement

of atmospheric halocarbons. A pair of test samples,

differing only slightly in concentration was sent

to each of sixteen laboratories. Statistical

analysis of the results reported by each laboratory

indicates systematic differences between laboratories

which are significantly larger than within laboratory

precision

1. INTRODUCTION

The persistence of certain anthropogenic substances in

the environment has generated concern over the long range

effects which such substances might have on the health and

well being of future generations. The relatively inert

halocarbons, which are largely man made, have increased in

use to the extent that they appear to constitute a permanent

component of the atmosphere. The reaction of these materials

with the environment at the earth’s surface appears to be of

little consequence and the health hazards of concentrations

many fold greater than currently exist could be easily tolerated. However, as time passes these substance may diffuse
in increasing quantities from the troposphere to the stratosphere where reactions with the ozone layer are quite likely

to occur. The ultimate effect of such reactions has been

the subject of much speculation and controversy. However,

if a prudent course is to be followed, to halt, or reverse,

the possible trend to increasing halocarbon concentrations

in the atmosphere, the time frame in which decisions must be

made requires that accurate assessment of the current conditions of the atmosphere, relative to these compounds, must

be made within a few years. Measurements must be made over

a wide area of the earth's surface and for a period of time

sufficient to quantify trends. Such measurements obviously

cannot be made by a single individual or laboratory but

are, and will be, made by many groups. These measurements

must be relatable one to another if valid conclusions are to

be drawn from them.

Concern for the measurement problem resulted in a workshop held at the National Bureau of Standards at Boulder,

jointly sponsored by the National Bureau of Standards,

National Aeronautics and Space Administration, and the National

Science Foundation. The goal of the workshop was to establish increased confidence in the halocarbon data measurements

[1], and to this end a program was suggested which involved

three basic phases. These were an assessment of the current

state-of-the-art of halocarbon measurements, recomendat ions

for changes in the measurement procedures based on the

evaluation of the state-of-the-art, and finally the production and distribution of reference materials which would

allow comparability between all laboratories making such

measurements

.

and

This report summarizes the results of the first phase

the conclusions drawn from the results have already been

2
used to solidify the course which the second and third

phases will follow.

The purpose of the first phase of the program was to

determine the state-of-the-art by means of a collaborative

test conducted among the principal laboratories currently

measuring atmospheric halocarbons. The test was not intended

to evaluate the performance of individual laboratories, but

rather was intended to reveal possible deficiencies in

measurement procedures related to the compounds of interest.

The study involved the distribution to the participating

laboratories of pairs of samples containing low concentrations

of dichlorodif luoromethane (F-12) and tr ichlorof luoromethane

(F-ll). In addition, the samples contained nitrous oxide,

which was considered to be of some importance to many of the

participants. The samples were prepared and analyzed to

assure that each pair of samples was identical to all other

pairs and that the difference between each sample in a pair

was constant throughout the entire set. It was further

necessary to be certain that the concentration remained the

same in each sample throughout the period of the test.

A tentative value for each constituent has been assigned

based on calibration procedures utilized at NBS during the

preparation of the samples. These values have been included

in this report but only with the same status as results from

any other participating laboratory; no greater weight has

been assigned than was given to other participants.

2. PREPARATION OF SAMPLES

The samples were prepared by compressing non-urban air

into fifty cleaned aluminum cylinders to a pressure of about

3
5.5 x 10 3 kiloPascals (800 psi) . The air being compressed

was periodically analyzed to be certain that it contained

reasonable amounts of the components of interest. Air,

free of detectable quantities of nitrous oxide and the

halocarbons was then added to twenty five of the cylinders

to a final pressure that resulted in a dilution of about 16

percent of the nitrous oxide and halocarbons originally

present. The samples were then analyzed for the concentration of nitrous oxide, halocarbons and for other halogenated

hydrocarbons.

The cylinders were filled to a relatively high pressure

in order that adequate samples would be available both for

the initial and final analysis at NBS and for the participant

without the occurrence of a large pressure drop in the

cylinder which might affect the concentration of the components because of desorption from the walls.

3. CYLINDERS AND CYLINDER PREPARATION

New, unused aluminum cylinders were cleaned, valved,

and evacuated under the direct supervision of NBS by a commercial supplier. A valve thread lubricant was used,

which was reported by the manufacturer to contain no halogens

The cylinders were filled preliminarily to a pressure of

about 6.9 x 10 3 kPa (1000 psi), and the contents were

examined. A large peak due to tr ichlorethylene was observed.

It was subsequently determined that this compound had been

used by the supplier to degrease the valves. Attempts were

made to remove the material by blowing down the cylinder,

heating the exterior with steam, and flushing and evacuating

several times. The treatment reduced the amount of trichlorethylene but not to a level that might not interfere with

subsequent analyses.

4
Consequently, all of the cylinders were blown down and

the valves disassembled. The valve components were washed

with ethanol and vacuum dried at 130 °C for 3 hours. The

valve bodies were not removed from the cylinder but were

heated in place with a heat gun.

The valves were reassembled and flushed with room air

followed by evacuation to a pressure of less than lkPa (0.01

atmosphere) . This treatment was repeated several times

after which a few cylinders were filled with air free of

tr ichlorethylene . These cylinders were examined over a period of several days and it was determined that the treatment substantially reduced the trichlorethy lene contamination

The filling of the cylinder with the final samples was then

begun

4. FILLING THE CYLINDER

The cylinders were filled using the system shown in

Figure 1. The air was drawn through a 12.7 mm (1/2 in)

copper tube mounted vertically on the roof of Building 236

(Hazards Laboratory) and projecting 3 meters above the roof

top. The Hazards Laboratory is located at the southern edge

of the NBS property in a relatively isolated location.

There are no activities in the building which would contribut

either nitrous oxide or halogenated hydrocarbons to the

atmosphere in the vicinity of the building. The surrounding

area is primarily open field and woodlands with no regularly

traveled roads in the vicinity.

The 12.7 mm (1/2 in) copper probe was connected to a 9.5 mm (3/8 in) copper tube leading from the roof to the

interior of the building at ground level. The probe and

lead line were both heated along their entire lengths with a

5
heat gun while air was drawn through them prior to use. Two

coarse particle filters were inserted in parallel to protect

the pump. The parallel installation was simply to reduce

the pressure drop in the inlet line. Two small stainless

steel diaphragm pumps were installed at the end of the lead

line to feed the main compressor inlet at 200kPa (30 psi)

.

The main compressor was a diaphragm pump in which the

sample contacts no lubricant nor any material other than

stainless steel, copper, and brass. The output of the main

pump was fed into a pair of low pressure stainless steel

cylinders which served to remove a large part of the water

from the sample. The compressed air, after water separation,

passed into a bank of four large steel cylinders of 42 L

capacity (1.5 ft 3 ). These cylinders were filled to a pressure of about 2.07 x 10 3 kPa (300 psi) as the first step.

The pressure in the water separator during the filling was

maintained at 2.07 x 10 3 kPa (300 psi) in order to prevent

condensation in the steel cylinder. When the pressure, in

the steel cylinder reached 2.07 x 10 3 kPa (300 psi) the main

pump was shut-off and the various valves shown were opened

and closed to direct the air in the steel cylinder to the

inlet of the main pump while the outlet was routed to the

high pressure water scrubber, then to the drier, and finally

to the bank of 50 small cylinders. The outlet of the main

compressor was maintained at about 1.4 x 10 4 kPa (2000 psi)

up to the valve beyond the high pressure drier. When the

pressure from the steel tanks at the inlet of the main

compressor dropped to 1000 kPa (150 psi) the compressor was

stopped and the valves were readjusted to refill the steel

cylinders to 2.07 x 10 3 kPa (300 psi). This sequence was

repeated until the pressure in the 50 small cylinders reached

5.5 x 10 3 kPa (800 psi). The time required was about one

6
week so that the samples represent the integrated concentration in the atmosphere during this period of time.

After each filling of the 50 small cylinders, the water

accumulated in the high pressure scrubber was blown off

through the valve at the bottom of the scrubber.

The high pressure dryer was filled with anhydrous

calcium sulfate. The possibility that calcium sulfate at

high pressure might adsorb trace materials from the sample

was investigated. It was found that some slight losses

occurred, but the bulk of the material passed through the

dryer without significant change in concentration.

After the fifty small cylinders were filled to 5.5 x

10 3 kPa (800 psi) , twenty five were removed from the manifold.

The remaining twenty five were diluted to a pressure of

about 6.4 x 10 3 kPa (925 psi) with air free of nitrous oxide

and the halocarbons F-ll and F-12. The dilution ratio is

approximately 1.16 to 1. The concentration of the three

substances in the diluted set of twenty five samples should

therefore be about 0.86 times that of the undiluted samples.

5. HOMOGENEITY VERIFICATION

5.1 Measurement Method and Standards

The analytical instrument used for the verification of

homogeneity and for subsequent assignment of a tentative

value to the samples was a commercial gas chromatograph

equipped with a

6

Ni electron capture detector. The detector

was operated at a temperature of 360 °C. A number of different column materials were tried, including activated alumina, Porapak Q, Chromasorb 102 and several types of porous

7
glass beads. All of these were satisfactory to some extent,

but the column found to give the best separation of F-ll

with a reasonably short retention time was a 0.92 m x 3.2 mm

(3' x 1/8") stainless steel column packed with porous glass

beads, 80/100 mesh, operated at 80°C. A 2.8 m x 3.2 mm

(9* x 1/8") stainless steel column packed with porous silica

O glass beads, 4 x 10 1 °m (40 A) pore size, 80/120 mesh, and

operated at 90 °C was used for F-12, and for nitrous oxide

the same column was used but the temperature was reduced to

80 °C. Full details of the analytical procedures may be

obtained directly from the authors.

It is possible to detect all three compounds under one

set of conditions on a single chromatogram. However,

because the purpose of these analyses was to establish the

relationship of the concentration of each compound in each

sample to all other samples, conditions were chosen independently for each compound such that the condition would give

the greatest precision for that compound. Therefore, while

these particular columns might not be ideal for determination

of all three components at once, it was possible to adjust

conditions to obtain good separation, to reduce overlap and

tailing and to produce sharp narrow peaks.

Attempts were made to measure the areas of the peaks

electronically but it was found that the peak height was in

general more reproducible and all of the values relating

samples to each other are based on manual measurement of

peak heights.

The carrier gas was a mixture of 5 percent methane in

argon. Flow rates were not set precisely but were controlled

by precise adjustment of the column head pressure to a value of 414 kPa (60 psi)

.

8
The values reported by NBS, as a participant in the

collaborative study, for the concentrations of F-ll and F-12

are based on comparison of the internal standard of each

lot, A and B, with standards prepared by static dilution of

a mixture containing the two halocarbons at concentrations

in the parts per million range. The starting mixture contained F-ll at 20 ppm and F-12 at 200 ppm. These were

diluted to the parts -per- trill ion range. In addition, a dynamic dilution system was used to dilute the starting

mixture to the range of the samples in order to define

roughly the response characteristics of the detector.

Further work is in progress to refine the dilution system

and to prepare independent standards starting with analyzed

samples of the two halocarbons.

The values for nitrous oxide are based on comparison of

the internal standard of each set with standards prepared by

static dilution of pure nitrous oxide and nitrogen.

5 . 2 Homogeneity Data

The entire set of samples was analyzed to determine the

homogeneity. This was done by selecting one sample at

random from each set of twenty five samples and comparing

all other samples in the set to that sample. All twenty

five samples in each set were compared for the halocarbon

content. The procedure in general consisted of alternating

analyses of the sample chosen at random, referred to as the

"internal standard", with several of the samples. Instrumental drift of the chromatograph was compensated for by

interpolating between standards to determine the instrument

response to the standard at the time when each sample was

analyzed. The signal for each sample was then divided by

the signal for the internal standard. This ratio was

multiplied by the tentative concentration assigned to the

9
Table 1. Analysis of Halocarbon in Each Sample,

Concentration in Parts per Trillion by Mole

Sample F-12 F- 11

No. A B A B

1 306 272 185 158

2 310* 273 184* 160

3 325 282 183 159

4 296 278 184 159

5 305 290 185 158

6 321 285 185 159

7 315 270 182 160

8 311 286 185 159

9 315 267 185 158

10 326 270 184 160

11 315 277 183 160

12 306 271 185 158

13 302 270 184 160

14 304 279* 183 159*

15 313 281 184 159

16 313 285 184 159

17 313 271 173 158

18 316 268 184 161

19 321 290 183 160

20 295 274 185 158

21 305 280 185 161

22 309 287 185 159

23 313 277 184 157

24 296 263 185 158

25 309 280 185 160

Ave 310 277 184 159

s . d

.

8(2.7%) 8 (2.9%) 1(0.5%) 1 (0.

Ratio of A to B 1.12 1.16

*Internal standards.

10

o\P
internal standard and the product was considered the tentative value for the analysis but not necessarily for the

concentration. The values for the analysis of each sample

in each lot for each halocarbon is shown in Table 1. The

lot marked "A" is the undiluted sample and "B M is the

diluted sample.

The standard deviation is based on all samples except

the internal standard and sample 17-A. The value for F-ll

in sample 17-A is obviously well below the average and well

outside of the limits of error and it has been excluded

from the exercise.

Table 2 is a summary of the results obtained on replicate analysis of several samples of both A and B series.

The standard deviation reflects the larger uncertainity in

the analysis for F-12 and confirms the homogeneity, within

the limits shown, of the concentration of F-12 and F-ll in

the two sets of samples.

11
Table 2. Replicate Analyses of Several Samples in

Both A and

Concentration in Parts

F-12

B Series

per Trillion by Mole

F-ll

Sample No. 2A 14B 2A A18 A21 B5 B13 B19

300 287 303 182 187 158 160 157

304 270 306 185 182 158 158 163

318 282 317 182 186 159 162 160

318 266 314 183 - 157 - -

292 277 - - - - - -

309 281 - - - - - -

308 276 - - - - - -

306 279 - - - - - -

317 264 - - - - - -

316 275 - - - - - - 321 287 - - - - - -

311 273 - - - - - -

311 278 - - - - - -

317 - - - - - - -

301 - - - - - - -

310 - - - - - - - Average 310 277 310 183 185 160 160

s.d. 8(2.6%) 7(2.5%) 7(2. 1%) 2(0.9%) 3(1.4%) 2(1.2%) 3(1

The values for F-12 in Sample 2A were obtained by comparison to

independent standards in much the same manner as the samples in both

A and B were analyzed. The two series for Sample 2A were obtained at

different times.

12
The analysis of nitrous oxide was performed in the same

manner as for the halocarbons except that not all of the samples

were analyzed before distribution to the participants. The

homogeneity among samples relative to the halocarbons, and

the results obtained on analysis of eight samples for nitrous

oxide indicated a similar degree of homogeneity among all

three components of interest. The results for nitrous oxide

are shown in Table 3.

Table 3. Analysis of Nitrous Oxide in Several Samples,

Concentration in Parts per Billion by Mole

Sample No. A B

1 302 259

2 299 -

3 298 -

7

- 263

12 298 255

14 - - 20 297 -

Ave 299 259

s . d. 2 (0.6%) 4

The uncertainty of the averages is less than the uncertainty of the average for replicate analyses of a single

sample which indicates that within the limits shown, each

set, A or B is homogenous within itself.

13
6. STABILITY OF SAMPLES

Assurance that the samples distributed for analysis

remain stable in concentration is critical to the entire

purpose of the collaborative test. Confidence that the

samples are stable can be deduced from several sources.

First, the homogeneity of each lot indicates that no random

and rapid losses are occurring. In general, loss of a component of a gas mixture in a cylinder is dependent on the

condition of the individual cylinder, and if such losses are

occurring in a number of cylinders, the concentrations

measured are different from each other by a greater amount

than the known imprecision of the method of analysis. The

larger the period of time between transfer of the sample

into the cylinder and the initial analysis, the greater will

be the range of values obtained. The samples in each lot

were "packaged" at least three weeks before the analyses

were completed and no evidence was found of instability of

the samples.

A second and more valuable source of information was

obtained by reanalysis of samples returned by the participants.

Unfortunately, all samples were not returned and several of

those that were returned were either contaminated or were

empty. Table 4 is a summary of the results obtained on

analysis for the halocarbons after return of the indicated

samples

.

14
Table 4. Analysis of Halocarbons in Samples after Return,

Concentration in Parts per Trillion by Mole

F- 12 F- 11

Sample No. A B A B

2 295 - 183 -

5 324 286 182 157

8 304 283 181 158

9 315 281 - -

10 317 274 186 160

13 308 270 183 159

14 302 275 - 159

18 310 288 185 156

20 307 273 180 160

22 312 265 183 155

23 302 278 182 162

24 317 276 183 161

25 322 281 182 158

Ave 310 278 183 159

s . d

9 (2.71) 7 (2.4%) 2 (0.9%) 2

15

o\°
The averages and uncertainties are essentially identical

to those obtained on the initial analysis and the conclusion

may be made that the samples did not change in composition

between the initial analysis and the time of analysis by the

participants

.

Samples which were returned but which are not included

in the results are samples numbered 4 and 11. Both number 4

sample cylinders were returned with the valves opened.

Sample 11 was found to be contaminated with a material which

seriously interfered with, and added to, the peak due to F-ll.

The contaminant was apparently in the valve and fluctuated

widely in concentration during a series of analyses of the

sample. The values reported by the participant, however,

appear to be valid and have been confirmed by his subsequent

analysis of a second set of samples for which the results

were identical to the analysis of the first set.

There is no evidence of loss of nitrous oxide in the

samples between the initial analysis of several samples and

the time of analysis of the samples that were returned. The

results obtained after return of the samples are shown in

Table 5.

16
Table 5. Analysis of Samples for Nitrous Oxide After Return.

Concentration in Parts per Billion by Mole

Sample No.

A B

5 300 255

8 298 256

9 296 258

10 298 262

13 299 262

18 — 266

20 300 255

22 302 264

23 302 262

24 305 254

25 296 254

Ave. 300 259

S.d. 3 (1.01) 4 (1.7%)

The averages agree quite well with the values prior

to distribution and the conclusion concerning stability

relative to the halocarbon apply equally to nitrous oxide.

7. PARTICIPATION

Sixteen laboratories participated in these collaborative

tests. Letters of invitation were issued to all attendees

at the "Workshop on Halocarbon Analysis and Measurement

Techniques" as well as a number of other laboratories known

to be actively engaged in measurements of halocarbons in the

atmosphere. Most all of those invited expressed interest

but some were unable to participate within the time period

designated for the Phase I tests.

17
The laboratories that met the requirements for participation are listed in the Appendix. They are believed to

represent groups of similar capability, hence their participation should furnish valuable information on the state of

the art of measurement of the components of interest.

Each participating laboratory was sent a set of two

test samples identified as FXA and FXB together with a serial number as already described. The laboratories were

requested to make a series of measurements on each sample,

using their own calibration methods and measurement procedures. They were instructed to report the mean value, the

number of measurements, and standard deviation of a single

measurement for each component. They were also requested to

describe the method of calibration and the measurement

procedure used. While each laboratory was encouraged to

measure all three components of interest, ^0, Fll and F12,

they were not excluded from the test if they could not

measure all of them.

8. RESULTS OF COLLABORATIVE TEST

The analytical results reported by the collaborating

laboratories are summarized in Tables 6, 7 and 8. The arbitrarily assigned laboratory designation is the same for each

set of measurements. The various columns list the number of

measurements, n, made by the laboratory, and the average

analytical result, x. The 95 percent confidence interval

for the average value was computed when possible, using the

standard deviation of a single measurement, s, as reported

by the laboratory. The tables also include the ratio of

concentrations FXA/FXB computed from the average values. In

addition, the consensus values, based on all of the measure18
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19

*Not

included

in

data

for

Youden

plot

because

this

laboratory

reported

after

computation.
Table

7.

Analytical

Results

for

Fll

Concentration

in

Parts

Per

Trillion

by

Mole

FXA

FXB

CQX

PP 3

Cn o rg vO rg O’) oo LO cn 00 LO vO cn vO

rH rH rH t-H Cn O t—H rH i-H rH rH to rH rH o rH

rH rH rH rH rH rH rH rH rH rH rH rH rH rH rH

u

o\® lo

cn

to cn rg rg rg cn vO to

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OO LOvO

Is

to O)

LO

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LO

cn

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to

IX

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20

Consensus

17

167

15

17

150

14

1.12

Max

197

180

Min

86

75

*Not

included

in

data

for

Youden

plot.
Table

8.

Analytical

Results

for

F12

Concentration

in

Parts

Per

Trillion

by

Mole

FXA

FXB

rH LO (XJ 03 rH (XJ rH to (XJ 03 O (XJ o

< pa rH rH rH 03 o rH rH rH rH rH 03 (X) o rH rH X X • PP PH rH rH rH rH rH rH rH rH rH rH rH rH rH

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o\° rH rH HLO

03

00 vo oo OO LO to tx tx to LO OO to vO tx vD X o (X) CD rH rH tx (XI (XJ LO tx vC 03 tx OO tO (XI (XJ (XJ (XJ to to to to to (XJ to (XJ (XJ

G tx oo O) LO LO LO LO vD

rH rH

•Hu

(XI to tx vO (XJ (XJ to (XJ O to

oV» rH (X) rH LO

LO

03

(XI O vO tX o 03 00 rH \C tx LO (XJ o vO IX \o to rH LO rH VC vO O IX rH rH rH rH tO (X) to (XJ (XJ to H* to to to to to

c 03 oo tx LO LO (XJ LO vO

to rH rH

c X o

g •H to o M 3

+J 03 to

a3 G G

s- * <D o H < pa Q W UL, C3 •“3 X hJ O Oh o- to

to G

03 CD O

-a n U

21

Max

419

396

Min

77

78

*Not

included

in

data

for

Youden

plot.
ments are reported as well as the maximum and minimum values

that ivere received from the participants.

The data were analyzed on the basis of the Youden plot

(2) as generalized by Mandel and Lashof (3) . This procedure

was proposed by Youden to distinguish between random flucuations of sample and/or measurement, and systematic errors.

Each laboratory is given a set of two samples of similar

composition and the result obtained on one is plotted with

respect to the result reported for the second sample. If

only random fluctuations of measurement and/or sample

composition are present, the data should be circularly

distributed about the intersection of the expected values

for the samples. When significant systematic errors are

present (bias) the points should be distributed in an

elliptical envelope and indeed along a 45° angle with the

x,y axes.

In the elliptical distribution, the perpendicular

distance of a point to the major axis of the ellipse is

related to the random error, while the distance of the

intersection of the perpendicular to the coordinates of the

expected value is related to bias. Accordingly, the length

of the major axis is related to the "between laboratory

variability", and the length of the minor axis to the

"material -laboratory interaction."

Experience has shown that a circular distribution is

rarely obtained but most frequently an elliptical distribution is observed. Ellipses in which the ratio of the major

axis to the minor axis is greater than 2, are considered to

be significant and indicate the existence of systematic

errors in the results reported by the collaborating laboratories .

22
The "best fitting ellipse" was computed by the procedure developed by Mandel and Lashof (3) and the parameters

are given in Table 9 and are graphically presented in figures

2, 3, and 4. The data from one laboratory was received after

the machine fitting of the ellipses. These values are

included in the values shown in Tables 6-8 but were not used

in the Youden plots. The grand mean values indicate the

consensus values for the samples, in which equal weight is

given to each reported value. Values are computed for the

major axis and the minor axis of ellipses that would be

expected to contain 99 percent and 95 percent, respectively,

of all values that would be reported by a very large number

of laboratories of which the present group is representative.

It will be noted that the ratios of these axes are

5.35 for N 9 0; 3.12 for Fll, and 14.8 for F12. These values

are considered to indicate that systematic errors predominate with respect to random errors in each case. The

graphical plots confirm this conclusion. However, it should

be emphasized that no rigid statistical parameters should be

inferred from the Youden-plot analysis. While the elliptical

distribution indicates the existence of significant bias

between values reported by the various laboratories, the

number of participants and the way the test was conducted

precludes the calculation of within- laboratory and betweenlaboratory variances. Moreover, since each laboratory used

its own-developed techniques and procedures, a detailed

analysis of such variance is not possible. The only conclusion that can be drawn is that significant systematic

errors do exist in results reported by various laboratories

and procedures need to be developed to minimize them, if

data reported by various laboratories are to be intercompared

23
Table

9.

Youden

Plot

Data

LO (VI LO •He CO rH tX

cdl*H • • • SIS LO to

rH

0

r1

O 0 0 60 vO o OJ e "d“ H- to <

e CTi tx to

•rH to to (VJ

o\° lo / V / V , v pa H H

cu CU Ch

Cl, CX Cm

•r—

v—J 00 v—

Ht ' ' o

cd o I—

1

LO

'r-'

,«=L O (VI t~H rH (VJ to

(xi rH rH

Ph Ph

e (V) 00 (VJ •H LO to s o\° cn

Cr>

•i—

i

00 o (VJ cd rx LO tx 2 (VI rH He pa O (VJ oo

cd X CT> LO [X

0 Pm s

(VJ rH (VI

e

cd < (VJ 00 00

5h X (VJ vO o

to rH to

24
The observed ratios of the concentration levels for

each constituent are of some interest, inasmuch as the lower

concentration sample was prepared by dilution of the one of

higher concentration. On the basis of manometric measurements,

a ratio of 1.16 would have been expected. However, it is

possible that the diluent air was not as pure as believed,

hence departures from the expected ratio are possible.

It is interesting to note that the consensus values

give a ratio of FSA/FSB of between 1.10 and 1.12 for all

three substances. The ratios obtained at NBS during the

homogeneity studies were: for ^0 - 1.15; for Fll - 1.16,

for F12 - 1.12. The NBS ratios for N^O and Fll are in

agreement with the expected values within the uncertainties

of measurement. The ratio found for the F-12 measurements

is lower than expected and may indicate the presence of F-12

in the diluent gas. However, the concentration of F-12

that would be necessary to account for the discrepancy would

appear to be unreasonable. In any event, a significant

departure from the expected ratio of 1.16 is believed to

constitute a reason to examine measurement procedures for

previously unsuspected measurement problems.

9. CONCLUSION

The overall conclusion that may be drawn from these

collaborative measurements of atmospheric samples is that

constituents occurring at the parts -per- trillion level of

concentration (-6 pg/m 3 ) can be measured in a given laboratory with a precision of 10 percent or better. However,

results reported by different laboratories can be expected

to vary by as much as ±40 percent.

25
This large error appears to be systematic in nature and

is probably due to differences in calibrations, and/or

sample handling techniques, although other causes cannot be

excluded at this time. The one first stated is the most

logical source of error since each laboratory would tend to

minimize its own handling and measurement errors if

calibration and analysis was done under similar conditions,

which appears to be the situation.

In Phase II of this program we propose to repeat the

collaborative tests with two additional samples and a reference sample which would be used as a benchmark for

all measurements that are reported. This would eliminate

the uncertainty due to variation in the composition of the

calibration gases used in each laboratory.

Another useful activity that would serve to identify

and minimize measurement biases, and perhaps also to improve

precision, is a workshop in which all participants would meet

to exchange their experiences in the measurements of these

samples. Such an exchange could uncover measurement problems not generally recognized, so that improvements in

technique could be adopted that would minimize these problems.

10. ACKNOWLEDGEMENT

This work was supported by the National Aeronautics and

Space Administration and by the Office of Air and Water

Measurements of the National Bureau of Standards.

26
11. REFERENCES

1. R. A. Rasmussen, D. J. Pierotti and J. Krasnec,

"Analysis of Halocarbons in the Atmosphere, Report

of a Workshop," Air Pollution Control Association,

69th Meeting, Portland, Oregon June 27-July 1, 1976.

2. W. J. Youden, "Graphical Diagnosis of Inter laboratory

Test Results", Industrial Quality Control, Vol. 15, No.

11, May 1959.

3. J. Mandel and T. W. Lashof, "Interpretation and

Generalization of Youdens Two-Sample Diagram,"

Journal of Quality Control, Vol. 6, No. 1, pp. 22-36,

January 1974.

27
12. APPENDIX

List of Participating Laboratories

Dr. Ralph J. Cicerone

University of Michigan

Space Research Laboratory

Ann Arbor, MI 48109

Robert K. Stevens

Arthur I. Coleman

United States Environmental Protection Agency

Environmental Sciences Research Center

Research Triangle Park, NC 27711

H. H. Gill

Dow Chemical USA

Michigan Division

Midland, MI 48640

Robert A. Gorski

E. I. DuPont de Nemours $ Co.

Organic Chemicals Department

Wilmington, DE 19898

Bennet J. Tyson

National Aeronautics and Space Administration

Ames Research Center

Moffett Field, CA 94035

Paul Fraser

Colin R. Ray

Commonwealth Scientific and

Industrial Research Organization

Division of Atmospheric Physics

Aspendale, Australia

Stewart A. Penkett

UKAEA Riseau Group

Environmental and Medical Sciences Division

AERE Harwell, Oxfordshire, ENGLAND

R. J. Lagomarsino

U. S. Energy Research and Development Administration

Health and Safety Laboratory

New York, NY 10014

Paul D. Goldon

Thane Thompson

National Oceanographic and Atmospheric Administration

Environmental Research Laboratories

Boulder, CO 80302

28
Lome Elias

National Research Council of Canada

National Aeronautical Establishment

Ottawa, Canada K1A0R6

Hanwant B. Singh

Stanford Research Institute

Menlo Park, CA 94025

H. I. Schiff

York UniversityFaculty of Science

Downsview, Ontario, Canada M3J1P3

J. E. Lovelock

Bowerchalke

Salisbury, Wiltshire, England SP56BQ

R. A. Rasmussen

Washington State University

Department of Chemical Engineering

Pullman, WA 99163

29
LOW

PRESSURE

RESERVOIR

30

Figure

1.

Schematic

Diagram

of

System

for

Falling

Sample

Cylinders
UOIina JOrf SUBj UT UOI^KaiUSDUOO - „a„ SldUIVS

c

o

M

u

4) a

</> +j

rt a

c

e

o

•H

4-> rtv4-> C

4)U

e

ou

<

4) rHa

G

n3 t/5

31

Figure

2.

Youden

Plot

of

Data

for

Nitrous

Oxide
o

1-0

(Nl o

o

rsj o

u~) uotxii^l -iod ui uoi^EjauaDU03

o

o

- ,.a„ a I dues

o

LO

32

50

100

ISO

2QQ

250

Sample

"A"

-

Concentration

in

Parts

Per

Trillion

Figure

3.

Youden

Plot

of

Data

for

Trichlorof

luoromethane

(F-ll)
o o o o o

o o o o o

Ln ^t rg i—i U0 TIIT-1 I -^d UI U0T1BJ1U3DU03 - 4i g ,, SlduiBS

33

0

100

200

. ;

300

400

500

600

Sample

"A"

-

Concentration

in

Parts

Per

Trillion

Figure

4.

Youden

Plot

of

Data

for

Dif

luorodichloromethane

(F-12)
U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 78-14802. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE 5. Publication Date Evaluation of Methodology for Analysis of Halocarbons

in the Upper Atmosphere : Phase I 6. Performing Organization Code

7. AUTHOR(S)

Ernest E. Hughes, William D. Dorko & John K. Taylor

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

National Atmospheric and Space Administration

Washington , D. C. 20546

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14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) This report describes the results of Phase I of a collaborative test to evaluate the state—of —the— art of measurement of the concentrations of halocarbons and nitrous oxide in the upper atmosphere. A pair of test samples, differing only slightly in concentration was sent to each of sixteen laboratories. Statistical analysis of the results reported by each laboratory indicates systematic differences between laboratories which are significantly larger than within laboratory precision.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Air Pollution, Atmospheric Freons, Halocarbon Analysis, Nitrous Oxide, Ozone layer, Trace Gas Analysis

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